Re: [CAD_CAM_EDM_DRO] Re: foam cutting current ?

The coefficient of resistance wire isn't as linear as platinum but it's
stable. You can design the current regulator to maintain a set temperature
once you've calibrated it.

Come to think of it, this will be an average over the length of the wire, so
if it's not all being used in cutting the foam, the temp wouldn't be
inaccurate. So if you string the wire on a tension mount with insulators,
then bring the current in with copper wire and clips. Then you put the
length of the resistance wire doing the cut in the controller, or the
controller could measure it if it was cold. Should get an even temperature
across the wire that way.

Just thinking out loud...

On 9/5/06, Graham Stabler <eexgs@...> wrote:
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
> <dave_mucha@...> wrote:
> >
> > Hi all,
> >
> > Is there a formula to help select the proper voltage and current for a
> > foam cutter ?
> >
> > Any special wire ?
> >
> > Dave
> >
>
> I don't know of any formulas but power disipated is I^2.R and the R
> will be a function of temperature itself so it might be a bit
> complicated. I suspect it is a rule of thumb situation.
>
> How long a wire do you need for cutting? A review of RC websites
> might give you an idea of the currents, its not more than a few amps.
> , lots of people seem to use 12v transformers driven from dimmers. A
> current regulated supply might be better.
>
> The best wire is nichrome, it has a high resistance and is very
> strong. I do manual cutting with a 0.25mm wire which is rather thin
> but reduces my "recast layer" meaning there is no melted surface on
> the foam. In CNC I think they tend to use the wire in a non contact
> mode so they always have this melted on layer which is fine if weight
> is not the issue and it can give a nice finish.
>
> Graham
>
>
>
>
>
>
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